Fluorinated surfactants for aqueous acid etch solutions

ABSTRACT

Novel aqueous, acid etch solutions comprising a fluorinated surfactant are provided. The etch solutions are used with a wide variety of substrates, for example, in the etching of silicon oxide-containing substrates.

FIELD OF THE INVENTION

The present invention is directed to certain fluorinated surfactants,and use thereof in aqueous acid etch solutions. The etch solutions areused with a wide variety of substrates, for example, in the etching ofsilicon oxide-containing substrates.

BACKGROUND

The use of microelectronic devices, such as integrated circuits, flatpanel displays and microelectromechanical systems, has burgeoned in newbusiness and consumer electronic equipment, such as personal computers,cellular phones, electronic calendars, personal digital assistants, andmedical electronics. Such devices have also become an integral part ofmore established consumer products such as televisions, stereocomponents and automobiles.

These devices in turn contain one or more very high qualitysemiconductor chips containing many layers of circuit patterns.Typically nearly 350 processing steps are required to convert a baresilicon wafer surface to a semiconductor chip of sufficient complexityand quality to be used, for example, in high performance logic devicesfound in personal computers. The most common processing steps ofsemiconductor chip manufacture are wafer-cleaning steps, accounting forover 10% of the total processing steps. These cleaning steps arenormally one of two types: oxidative and etch (or both). Duringoxidative cleaning steps, oxidative compositions are used to oxidize thesilicon or polysilicon surface, typically by contacting the wafer withaqueous peroxide or ozone solution. During etch cleaning steps, etchingcompositions are used to remove native and deposited silicon oxide filmsand organic contaminants from the silicon or polysilicon surface beforegate oxidation or epitaxial deposition, typically by contacting thewafer with aqueous acid. See, for example, L. A. Zazzera and J. F.Moulder, J. Electrochem. Soc., 136, No. 2, 484 (1989). The ultimateperformance of the resulting semiconductor chip will depend greatly onhow well each cleaning step has been conducted.

Microelectromechanical systems (MEMS) (also called micromachines ormicromechanical devices) are small mechanical devices that can be madeusing traditional integrated circuit manufacturing techniques. Typicaldevices include motors, gears, accelerometers, pressure sensors,actuators, mirrors, biochips, micropumps and valves, flow sensors andimplantable medical devices and systems. The manufacture of MEMS mayresult in a chip, or die, which contains the moving pieces of the devicemade from silicon or polycrystalline silicon (polysilicon) encased insilicon oxide. The die can also contain the circuitry necessary to runthe device. One of the final steps in the manufacture of silicon-basedMEMS is commonly referred to as “release-etch” and consists of anaqueous etch utilizing hydrofluoric acid (HF) to remove the siliconoxide to free, or “release”, the silicon or polysilicon pieces and allowthem to move.

For etch cleaning steps, the composition of choice has been diluteaqueous hydrofluoric acid (HF) and, to a lesser extent, hydrochloricacid (HCl). Currently, many semiconductor fabricators employ an“HF-last” etch cleaning process consisting of an etching step usingdilute aqueous HF to etch oxides.

In the wet etching of an oxidized silicon substrate, aqueous hydrogenfluoride or a mixture with an onium fluoride complex may be used as anetchant. The onium fluoride present serves to adjust the etching rateand stabilize the solution to variation in HF concentration. Thesebuffered oxide etch solutions, or BOEs have a high surface tension and,as a result, may not adequately wet a substrate or penetrate microscopicsurface features.

SUMMARY OF THE INVENTION

The present invention provides an aqueous etch solution comprising anacid; and a surfactant of the formula:R_(f)—Q—R¹—SO₃ ⁻M⁺  (I)wherein R_(f) is a C₁ to C₁₂ perfluoroalkyl group, R¹ is—C_(n)H_(2n)(CHOH)_(o)C_(m)H_(2m)—, wherein n and m are independently 1to 6, and o is 0 or 1, and wherein R¹ optionally contains a catenaryoxygen or nitrogen atom; M⁺ is a cation; and Q is —O—, or —SO₂NR²—,wherein R² is H, an alkyl, aryl, hydroxyalkyl, aminoalkyl orsulfonatoalkyl. The solution may further comprise an onium fluoridecompound, such as ammonium fluoride, and may further comprise a secondfluorinated surfactant, such as perfluoroalkylsulfonamido salt.

The fluorinated surfactant is sufficiently stable in the aqueous acidetch solution, and advantageously reduces the surface tension thereof sothat nanoscale features may be effectively provided to a siliconsubstrate, such as an integrated circuit and is soluble in the aqueousacid solution. The solution of the instant invention provides one ormore of the following advantages; the solution has the same etch rate asconventional etch solutions, possesses low surface tension resulting inlow contact angles between the solution and substrate. In addition it isnon-foaming, low in particulates that may contaminate a substrate andleaves low or no surface residues on rinse. It also offers improvedstability of performance when filtered or after extended storage andaffords excellent substrate surface smoothness.

The etch solution of the present invention is particularly suitable forthe etching of oxidized silicon substrates, where the acid ishydrofluoric acid (HF) and/or an onium fluoride complex thereof. Othersubstrates, including metals and oxides may also be etched and cleanedby appropriate selection of acid or mixtures of acids.

In one aspect, this invention relates to an etch solution useful insemiconductor and integrated circuit manufacture, the compositioncomprising a fluorinated surfactant, hydrogen fluoride and/or oniumcomplex thereof. Advantageously, the present invention provides anaqueous etch solution useful for etching, and removal of residues, thatcontains a relatively low concentration of surfactant, but effectivelywets the substrate and has an efficient rate of etching. Substratesuseful in the present invention include silicon, germanium, GaAs, InPand other III-V and II-VI compound semiconductors. It will beunderstood, due to the large number of processing steps involved inintegrated circuit manufacture, that the substrate may include layers ofsilicon, polysilicon, metals and oxides thereof, resists, masks anddielectrics. The present invention is also particularly useful in theetch and release of silicon-based microelectromechanical (MEMS) devices.The etch cleaning and drying of MEMS has similar issues to those forsemiconductor chip manufacture.

In another aspect, this invention relates to an etch process forsubstrates by contacting a substrate with a homogeneous etch solutioncomprising the fluorinated surfactant and acid for a time sufficient toachieve a predetermined degree of etching. In a preferred embodiment,this invention relates to a etch process for substrates by contacting anoxidized silicon substrate with a homogeneous etch solution comprisingthe fluorinated surfactant, HF and/or onium fluoride complex for a timesufficient to achieve a predetermined degree of etching. The presentinvention provides an etch solution with low surface tension that easilypenetrates the intricate microstructures and wets the surfaces onsilicon substrates. If desired, the etch process may further comprisethe step of rinsing the etch solution from the surface of the etchedsubstrate, and the step of drying the substrate.

In another aspect, the present invention provides a buffered oxide etchsolution (BOE, also known as buffered hydrogen fluoride or BHF)comprising an aqueous solution of the above-described fluorinatedsurfactant, hydrogen fluoride and ammonium fluoride. Such solutions areparticularly useful in etching of oxidized silicon due to the highSiO₂/Si etch selectivity.

It is to be understood that the recitation of numerical ranges byendpoints includes all numbers and fractions subsumed within that range(e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). It is to beunderstood that all numbers and fractions thereof are presumed to bemodified by the term “about.” It is to be understood that “a” as usedherein includes both the singular and plural.

The term “alkyl” refers to straight or branched, cyclic or acyclichydrocarbon radicals, such as methyl, ethyl, propyl, butyl, octyl,isopropyl, tert-butyl, sec-pentyl, and the like. Alkyl groups include,for example, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or preferably 1to 6 carbon atoms.

The term “aryl” refers to monovalent unsaturated aromatic carbocyclicradicals having a single ring, such as phenyl, or multiple condensedrings, such as naphthyl or anthryl.

The term “perfluoroalkyl” refers to a fully fluorinated monovalentstraight or branched, cyclic or acyclic, saturated hydrocarbon radicalsuch as, for example, CF₃—, CF₃CF₂—, CF₃CF₂CF₂—, (CF₃)₂CFCF₂CF(CF₃)CF₂—,CF₃CF(CF₂CF₃)CF₂CF(CF₃)CF₂—, and the like. One or more non-adjacent—CF₂— groups may be substituted with a catenary oxygen or nitrogen atomsuch as, for example, CF₃CF₂OCF(CF₃)CF₂—, and the like. Perfluoroalkylgroups include, for example, 1 to 12 carbon atoms, preferably 3 to 6carbon atoms.

DETAILED DESCRIPTION

Compositions of this invention, comprising a fluorinated surfactant, andan acid such as hydrogen fluoride and/or onium fluoride complex, areuseful in the various etch operations performed on substrates such asthose that may be required for operations in the manufacture ofsemiconductors. As used herein “substrate” will refer to wafers andchips used in semiconductor manufacture, including silicon, germanium,GaAs, InP and other III-V and II-VI compound semiconductors. For siliconand SiO₂ substrates, the compositions can effectively converthydrophilic silicon oxides to soluble or volatile silicon fluorides.

Other substrates, such as metals may also be etched by appropriateselection of the acid. The fluorinated surfactant effectively reducesthe surface tension of the aqueous acid, allowing effective wetting ofthe substrate.

The etch composition and method of this invention can offer enhancedwetting, which is especially important in small geometry patterns andfor features with large aspect ratios, reduced particulatecontamination, and reduced surface roughness all leading to improvementsin manufacturing efficiency by lowering defects to increase wafer yield,by decreasing cleaning times to increase wafer production or by allowingfor longer etch bath life by reducing filtration losses of surfactant.

The improved performance is due, in part, to the low surface tension ofthe etch solution due to the fluorinated surfactants used, whichcontributes to the improved wetting of the surfaces. The surfacetensions of the etch solutions are generally less than 50 dynes/cm,preferably less than 23 dynes/cm and most preferably between 15 and 20dynes/cm when measured at 25° C.

The present invention provides an aqueous etch solution comprising anacid and a surfactant of the formula:R_(f)—Q—R¹—SO₃ ⁻M⁺  (I)wherein

-   R_(f) is a C₁ to C₁₂ perfluoroalkyl group, optionally containing    catenary oxygen or nitrogen atoms,-   each R¹ is independently —C_(n)H_(2n)(CHOH)_(o)C_(m)H_(2m)—, wherein    n and m are independently 1 to 6, and o is 0 or 1, and wherein R¹    optionally contains a catenary oxygen or nitrogen atom;-   M⁺ is a cation; and-   Q is —O—, or —SO₂NR²—, wherein R² is H, an alkyl, aryl,    hydroxyalkyl, sulfonatoalkyl or aminoalkyl. Preferably, Q is    —SO₂NR²— wherein R² is a hydroxyalkyl or aminoalkyl.

The R_(f) group is a perfluorinated alkyl group having from 1-12 carbonatoms, with 3 to 6 carbon atoms preferred. The R_(f) perfluorinatedalkyl groups may be unbranched, branched, or acyclic, cyclic andpreferably are unbranched. Catenary heteroatoms such as divalent oxygen,trivalent nitrogen or hexavalent sulfur may interrupt the skeletalchain, (i.e. replace one or more non-adjacent —CF₂—groups). When R_(f)is or contains a cyclic structure, such structure preferably has 5 or 6ring members, 1 or 2 of which can be catenary heteroatoms. The alkyleneradical R_(f) is also free of ethylenic or other carbon-carbonunsaturation: e.g., it is a saturated aliphatic, cycloaliphatic orheterocyclic monovalent group.

The R² group of —SO₂NR²— (Q group) may be an H, an alkyl, hydroxyalkyl,aminoalkyl, or a sulfonatoalkyl group of the formula —R¹—SO₃ ⁻M⁺. Thus,R² may be an alkyl group of the formula —C_(p)H_(2p+1), a hydroxyalkylgroup of the formula —C_(p)H_(2p)—OH, or an aminoalkyl group of theformula —C_(p)H_(2p)—NR³R⁴, a sulfonatoalkyl group of the formula—C_(p)H_(2p)—SO₃ ⁻, where p is an integer of 1 to 12, preferably 1 to 6,and R³ and R⁴ are independently H or alkyl groups of 1 to 12 carbonatoms, preferably 1 to 6 carbon atoms.

The R² group may also comprise an aryl group having from 5 to 12 ringatoms, for example phenyl or naphthyl rings. Substituted aryl groups,such as alkyl substituted aryl groups of the formulaC_(p)H_(2p+1)-(Aryl)- are also contemplated, as are arylalkylene groupsof the formula —C_(p)H_(2p)-(Aryl).

The invention therefore provides etch solutions comprising fluorinatedsurfactants of the formula:

wherein R_(f), R¹ and M⁺ are as previously defined, p is 1 to 6, Ar isan aryl group, and Z is H, —OH, —SO₃ ⁻, an aryl group (Ar), or —NR³R⁴,where R³ and R⁴ are independently H or alkyl groups of one to six carbonatoms.

Many previously known fluorinated surfactants contain perfluorooctylmoieties, such as the perfluorooctanesulfonate anion (PFOS). It has beenreported that certain perfluorooctyl-containing compounds may tend tobio-accumulate in living organisms; this tendency has been cited as apotential concern regarding some fluorochemical compounds. For example,see U.S. Pat. No. 5,688,884 (Baker et al.). As a result, there is adesire for fluorine-containing surfactants which are effective inproviding desired performance, and which eliminate more effectively fromthe body (including the tendency of the composition and its degradationproducts).

It is expected that the surfactants of the present invention, whichcontain anions with relatively short perfluoroalkyl segments (<8perfluorinated carbon atoms), when exposed to biological, thermal,oxidative, hydrolytic, and photolytic conditions found in theenvironment, will break down to functional, short chain fluorocarbondegradation products that will not bio-accumulate. For example,compositions of the present invention comprising a perfluorobutylmoiety, such as CF₃CF₂CF₂CF₂—, are expected to eliminate from the bodymore effectively than perfluorohexyl- and much more effectively thanperfluorooctyl-. For this reason preferred embodiments of the R_(f)group in Formula I include perfluoroalkyl groups, C_(m)F_(2m+1)—containing a total of 3 to 6 carbon atoms.

With respect to R¹, the indicated alkylene group may further contain acatenary (i.e. in chain) oxygen or nitrogen group whereby a —CH₂— groupis replaced by —O— or —NR⁵—, wherein R⁵ is an H—, or a C₁ to C₆ alkylgroup. If desired, the catenary nitrogen group may be a quaternary aminegroup of the formula —N(R⁵)₂ ⁺—, where each R⁵ group is independently analkyl group of 1 to 6 carbons. Useful catenary amine groups may include,for example —NH—, —N(CH₃)—, —N(C₃H₆)—, —N(CH₃)₂ ⁺—, —N(CH₃)(C₄H₉)⁺— andthe like. Thus, the catenary amine group may comprise an in-chainsecondary, tertiary or quaternary nitrogen atom. It is preferred thatsuch catenary atoms are not alpha to a —(CHOH)— group, if present andare not alpha to a heteroatom, such as is found in the Q group and —SO₃⁻ group of Formula I.

With respect to Formula I, M⁺ represent an inorganic or organic cation.Suitable inorganic cations include metal cations, including transitionmetal cations, alkali- and alkaline earth metal cations and ammoniumcations such as NH₄ ⁺. Suitable organic cations include onium cationssuch as ammonium, including primary, secondary, tertiary and quaternaryammonium cations, as well as sulfonium, and phosphonium cations. Formany etching applications, such as in the preparing of semiconductors,metals may have a deleterious effect on the subsequent electronicperformance of the devices and for this reason, ammonium cations,especially NH₄ ⁺ and quaternary ammonium cations are preferred.

In general, materials of the invention are prepared by first generatingan anion from the appropriate fluorochemical moiety in a polar solvent.The anion is typically generated in-situ by reaction of the appropriatefluorochemical moiety with either a strong base, or a fluoride ion. Forexample, where Q is —O—, a fluoroalkoxide anion of the formula R_(f)—O⁻is generated by treating the corresponding acid fluoride (R_(f)—CO—F)with fluoride ion. Alternatively, where Q is —SO₂NR²—, a sulfonamidesalt may be generated by reacting a compound of the formulaR_(f)—SO₂NR²H with strong base to form a nitrogen-centered anion of theformula R_(f)—SO₂N⁻R². These anions may be further reacted with anelectrophile containing either a sulfonate group, or containing anascent sulfonate group (i.e. a sultone) resulting in compositions ofthe invention. Further details regarding the preparation of compounds ofFormula I may be made with reference to the examples.

The HF may be aqueous HF per se (i.e. diluted 49% HF), or may be used inthe form of an onium fluoride complex. Such complexes, known as “oniumpoly(hydrogen fluorides)” have the general formula BH⁺(HF)_(x)F^(−,)where B is an electron-pair donor base and x is an integer generallyfrom 1 to 10, and include oxonium-, ammonium-, pyridinium-, andphosphonium-poly(hydrogen fluorides). Such onium complexes are lessvolatile, less corrosive, and are normally liquids at room temperatures.Many such onium complexes are stable liquids that resist the loss of HFeven during distillation. Further information regarding useful oniumcomplexes may be found in Synthetic Fluorine Chemistry, George A. Olah,et al., editors, “Fluorination with Onium Poly(hydrogen fluorides): thetaming of anhydrous hydrogen fluoride for synthesis”, John Wiley andSons, New York, N.Y., pp. 163-204.

The HF useful in compositions and processes of this invention, whetheraqueous HF or an aqueous onium complex, is preferably substantially freeof other contaminants such as metals, particulates and non-volatileresidues in order to effectively etch the silicon surface at the maximumrate during the manufacturing process and not leave residues.

The etch solution may be prepared by combining, in any order, the acid(the aqueous hydrogen fluoride and/or the onium fluoride complex in thecase of silicon substrates) and the fluorinated surfactant. For oxidizedsilicon substrates, the concentration of hydrogen fluoride may varywidely, i.e. from 0.1 to 49 wt. %, depending on the substrate and theetch rate desired. Generally, the concentration of HF is form about 0.1to 10 wt. %. If an onium fluoride complex, such as ammonium fluoride, issubstituted for all or part of the HF, the amount of the onium fluoridemay be determined by the HF acid equivalent.

If desired, the etch solution may further comprise an organic solvent.In many instances the use of an organic solvent may improve theperformance, particularly the post-filtration performance, of the etchsolution by improving the solubility of the fluorinated surfactant inthe aqueous HF solution. It is believed that organic solvents mayadvantageously lower the critical micelle concentration of thesurfactant. Useful organic solvents may include polar solvents such asethers, such as diethyl ether or tetrahydrofuran, polyethers such asglymes, alcohols, esters, dimethylformamide, acetonitrile, acetone,dimethylsulfoxide and carbonates. Solvent selection may be made byreference to Shah, et al., Semiconductor International, October 1988.

If desired, the etch solution may further comprise a second surfactant,in addition to the surfactant of Formula I. Such second surfactantsinclude both fluorinated and non-fluorinated surfactants such as areknown in the etching art. Reference may be made to Kikuyama et al., IEEETransactions on Semiconductor Manufacturing, Vol. 3, 1990, pp 99-108,incorporated herein by reference. Generally, the second surfactant maycomprise 0 to 80 weight % of the total surfactant; the total amount offirst and second surfactants comprising 10 to 1000 parts per million.

A particularly useful class of second surfactants isperfluoroalkylsulfonamido salts, including those of the formula:R_(f)—SO₂N⁻—R⁶M⁺  (II)wherein R_(f) is a C₁ to C₁₂ perfluoroalkyl group as previouslydescribed for the surfactants of Formula I, R⁶ is H, an alkyl group, anaryl group, a hydroxyalkyl group or an aminoalkyl group each having oneto six carbon atoms, or an aryl group having 6 to 12 ring atoms, and M⁺is a cation. Preferably, R⁶ is H or a hydroxyalkyl group, and preferablyM⁺ represents an ammonium cation, including NH₄ ⁺, and primary,secondary, tertiary and quaternary ammonium cations. Etch solutionscontaining mixtures of the fluorinated surfactant of Formula I andperfluoroalkylsulfonamido salts have been found to provide lower surfacetension solutions than can be achieved using either surfactant alone.Fluorochemical sulfonamides corresponding to Formula II may be preparedas described in U.S. Pat. No. 4,370,254 (Mitschke et al.)

The invention provides a process for etching a substrate by contactingthe substrate with the etch solution of the invention for a time and ata temperature sufficient to effect the desired degree of etching.Preferably, the substrate is an oxidized silicon substrate and the etchsolution is a buffered oxide etch solution as described herein. Normallyan oxidized silicon substrate is etched at 15 to 40° C. If desired, theetch process may further comprise the step of rinsing the etch solutionfrom the etched substrate. In one embodiment, the solution may be rinsedwith water, and preferably deionized water. In another embodiment, theetch solution is slowly replaced with deionized water in a gradient etchprocess.

The etch process may further including a drying step whereby the rinsesolution is removed from the surface of the etched substrate such as bythe application or heat, forced air, immersion in a solvent bath, suchas an alcohol bath, or immersion is the heated vapors of a solvent suchas an alcohol.

For the etching of SiO₂ substrates, a mixture of HF and an oniumfluoride complex is preferred to stabilize the solution and to reducethe variation in the amount of free HF. Such buffered oxide etchsolutions may comprise 0.1 to 10 weight % HF and 20 to 40 weight % ofammonium fluoride. Such solutions will generally have pH values of from2 to 7.5.

The surfactant is used in amounts sufficient to reduce the surfacetension of the solution to the desired degree. For wet etching ofsilicon substrates, the surfactant is generally used in amountssufficient to reduce the surface tension of the resulting solution to 50dynes/cm or less, preferably 23 dynes/cm or less. Generally the solutioncomprises 10 to 1000 parts per million of surfactant, and is preferably100 to 500 parts per million. Below 10 parts per million the solutionmay not exhibit the desirable reduced surface tension and large contactangle on silicon substrate. Above 1000 parts per million, there islittle improvement in the properties of the solution or the performancein etching.

The buffered oxide etch solution comprising an aqueous solution offluorinated surfactant, hydrogen fluoride and onium fluoride, preferablyammonium fluoride, may be used to etch the surface of a silicon wafer.In particular, the solution may be used to etch a SiO₂ surface having aresist mask. Conventional buffered oxide etch solutions often failed towet, and subsequently etch, fine features of such devices leading todefects.

BOE etchants are used in standard oxide etch processes in the IC andMEMS manufacture. While the isotropic etching behavior of BOE can limitits utility, the high selectivity for etching of silicon oxide (SiO₂)over silicon (Si) is a tremendous advantage over dry etching processes,such as reactive ion etch (RIE). Conventional BOE solutions fail tofully flow into the small contact holes and some of the oxide remains,thereby creating defects.

Other substrates may also be etched by appropriate selection of the acidor acid mixture. Gold, indium, molybdenum, platinum and nichromesubstrates may be etched with a mixture of hydrochloric and nitricacids. Aluminum substrates may be etched with a mixture of phosphoricand nitric acids, and may optionally include acetic acid as a buffer.Silicon substrates may be etched with a mixture of hydrofluoric, nitricand acetic acids. In general, the fluorinated surfactant is used inamounts described for the buffered oxide etch previously described. ASIRTL etch solution may be prepared using a mixture of chromium trioxideand hydrofluoric acid to determine defects in single crystal silicon.

The objects, features and advantages of the present invention arefurther illustrated by the following examples, but the particularmaterials and amounts thereof recited in these examples, as well asother conditions and details, should not be construed to unduly limitthis invention. All materials are commercially available or known tothose skilled in the art unless otherwise stated or apparent.

EXAMPLES

Description/Structurer Descriptor and or Formula Availability Adogen ™methyltrialkyl(C8-C10) Sigma-Aldrich 464 ammonium chloride Milwaukee, WICHPS 3-chloro-2-hydroxy-1- Sigma-Aldrich propanesulfonate sodium salt;ClCH₂CH(OH)CH₂SO₃Na⁻H₂O DMAPA dimethylaminopropylamine; Sigma-AldrichH₂N(CH₂)₃N(CH₃)₂ Aniline NH₂C₆H₅ Sigma-Aldrich DME dimethoxyethane;Sigma-Aldrich CH₃OCH₂CH₂OCH₃ Forfac ™ (C₆F₁₃CH₂CH₂SO₃H) Atofina 1033DChemicals Philadelphia, PA FC-23 FLUORAD ™ FC-23; C₃F₇CO₂H 3M Company,St. Paul, MN Hexane CH₃(CH₂)₄CH₃ Sigma-Aldrich MTBE methyl-t-butylether; Sigma-Aldrich CH₃OC(CH₃)₃ n-octylamine CH₃(CH₂)₇NH₂ Sigma-Aldrichtriethylamine N(C₂H₅)₃ Sigma-Aldrich PBSF perfluorobutanesulfonylfluoride; Sigma-Aldrich C₄F₉SO₂F 1,4-butane sultone

Sigma-Aldrich 1,3-propane sultone

Sigma-Aldrich

C₄F₉SO₂NH(CH₂)₃N(CH₃)₂ can be prepared essentially according to U.S.Pat. No. 5,085,786 (Alm et al.) replacing C₆F₁₃SO₂F with C₄F₉SO₂F.

C₄F₉SO₂NH(C₂H₅) can be prepared essentially according to WO 01/30873 A1,Example 1A, replacing NH₂CH₃ with an equimolar amount of NH₂C₂H₅.

FC-17 can be prepared essentially according to WO 0 1/30873 A 1 Example1.

TEST METHODS

Test Procedure I—Surface Tension Determination

All surface tensions were determined using a Kruss K12 Tensiometer. Theprogram was run using a Wilhelmy platinum plate (PL12) and plasticsample vessel (HDPE). All parts referenced above, except for the plasticsample vessel, but including instrument and computer are available fromKruss USA, Charlotte, N.C.

Preparation of FC-1; C₄F₉SO₂N(C₂H₅)C₃H₆SO₃Li

A 500 mL round bottom flask equipped with a condenser, heating mantleand stirrer was charged with C₄F₉SO₂NH(C₂H₅) (15.0 g, 0.0458 moles),LiOH.H₂O (2.1 g; 0.05 moles) and MTBE (100 mL). The ensuing mixture washeated at reflux temperature, with stirring for 1.5 hours. After coolingto room temperature, the mixture was filtered. The clear, colorlessfiltrate was combined with 1,3-propane sultone (6.12 g; 0.05 moles) andheated to about 50° C. for 1.5 hours causing precipitation of a whitesolid. After cooling to room temperature, the white solid was isolatedby filtration of the MTBE suspension by suction through a sintered glassfrit and washing of the precipitate with two 150 mL portions of MTBE toremove possible residual soluble starting materials. The solid was driedpartially by suction and then further dried in a vacuum oven at 50-60°C., 10⁻² torr for about one hour. A white crystalline solid was obtained(13.75 g; 66% yield). The ¹H NMR spectrum recorded at 200 MHz ind₆-acetone was consistent with the structure of C₄F₉SO₂N(C₂H₅)C₃H₆SO₃Li.

Preparation of Intermediate C₄F₉SO₂NH₂

A 3-necked round bottom flask fitted with a cold finger condenser (−78°C.), an overhead stirrer, thermocouple and a plastic tube for gasaddition was charged with perfluorobutanesulfonyl fluoride (PBSF; 500.0g; 1.6 moles; available from 3M Company, St Paul, Minn.), isopropylether (600 mL; available from Sigma-Aldrich) and placed in a bath ofroom temperature water. Ammonia gas (90.0 g; 5.3 mole) was added throughthe tube over a period of 3 hours at a rate such that dripping off the−78° C. condenser was not observable,. The final temperature of themixture was 13° C.

The mixture was allowed to stir overnight with warming to roomtemperature, then the solvent was distilled at atmospheric pressure.When the pot temperature reached 95° C., the temperature setpoint waslowered to 74° C. and deionized water added (400 mL) followed bysulfuric acid (100 g conc; 95%) at a rate to maintain the temperaturebelow 85° C. The batch was stirred for about 15 minutes then the upperaqueous phase was removed. The resulting solids were washed with aqueoussulfuric acid (50.0 g; conc; 95% in 400 mL water), then with deionizedwater (500 mL).

The mixture was heated and solvent removed under vacuum with waterflowing through the condenser until the batch temperature reached 75° C.The solid was isolated by distillation at 12 torr and temperature of120° C. to 160° C. 454 g of white to créme colored solid, C₄F₉SO₂NH₂(96% yield) was obtained.

Preparation of Intermediate C₄F₉SO₂NH(C₂H₄OH)

A 5 L round bottom flask equipped with an overhead stirrer,thermocouple, and reflux condenser was charged with C₄F₉SO₂NH₂ (2000.0g; 6.69 moles), ethylene carbonate (245 g; 2.78 moles), and sodiumcarbonate (48.5 g; 0.45 moles; Na₂CO₃). The mixture was heated, withstirring, at 120° C. for one hour. More ethylene carbonate (154 g; 1.75moles) was added and the mixture was heated for an additional 1.5 hours.After additional ethylene carbonate (154 g; 1.75 moles) was added thebatch was then heated for an additional 4.5 hours. The mixture wascooled to 89° C., and deionized water (1000 mL) was added, followed bysulfuric acid (56 g; concentrated). The batch was agitated for 30minutes and stirring was discontinued, allowing separation into twophases.

The upper aqueous phase layer was removed by vacuum aspiration anddeionized water (1000 mL) was added to the remaining organic layer andthe mixtures was stirred at 89° C. for an additional 30 minutes. Thereaction mixtures was poured into a separatory funnel and the lowerorganic phase was separated from the upper aqueous phase to yield 2163 gof crude C₄F₉SO₂NH(C₂H₄OH).

GC analysis indicated that the crude material contained 66% of thedesired material. Crude C₄F₉SO₂NH(C₂H₄OH) was placed in a three-literflask equipped with an overhead stirrer, thermocouple, vacuum gauge, anda six plate sieve tray distillation column along with associateddistillation head and receiver. Water was removed under reduced pressureuntil the pot temperature reached 87° C. (@ 29 mm Hg), followed byfractional distillation. High purity C₄F₉SO₂NH(C₂H₄OH) (greater than 95%gc assay) was collected at head temperatures of 120-134° C., pottemperatures of 156-170° C., and vacuum of 4-9 mm Hg; A total of 1075 gwas isolated (correcting for % conversion, the yield was 74%).

Preparation of FC-2; C₄F₉SO₂N(C₂H₄OH)C₃H₆SO₃Li

C₄F₉SO₂N(C₂H₄OH)C₃H₆SO₃Li was prepared essentially according to theprocedure described in Preparation 1 with the exception thatC₄F₉SO₂NH(C₂H₅) was replaced with C₄F₉SO₂NH(C₂H₄OH) (4.2 g; 0.012 moles;as prepared above), and the corresponding amounts of the following wereused: LiOH—H₂O (0.56 g; 0.013 moles), MTBE (50 mL) and1,3-propanesultone (1.64 g; 0.013 moles). A white crystalline solid wasisolated (3.39 g; 58.9% yield).

Preparation of FC-3; C₄F₉SO₂N(C₂H₄OH)C₄H₈SO₃Li

C₄F₉SO₂N(C₂H₄OH)C₄H₈SO₃Li was prepared essentially according to theprocedure described in Preparation 1 with the exception that thecorresponding amounts of the following were used: usingC₄F₉SO₂NH(C₂H₄OH) (4.2 g; 0.012 moles; as prepared above), LiOH.H₂O(0.565 g; 0.013 moles), MTBE(50 mL), and (75mL), and 1,3-propane sultonewas replaced with 1,4-butanesultone (1.83 g; 0.013 moles). Additionally,after evaporating most of MTBE by boiling at atmospheric pressure, DMEwas added and reflux was resumed at 85° C. for 1 hour resulting inprecipitation of a white solid. The white solid was isolated (1.39 g;23.5% yield).

Preparation of FC-4; C₄F₉SO₂N(H)C₄H₈SO₃Li

C₄F₉SO₂N(H)C₄H₈SO₃Li was prepared essentially according to the proceduredescribed in Preparation 3 replacing C₄F₉SO₂NH(C₂H₄OH) with C₄F₉SO₂NH₂(15.0 g; 0.05 moles), and the corresponding amounts of the followingwere used: LiOH—H₂O (2.32 g; 0.055 moles), MTBE (100 mL), DME (100 mL),and 1,4-butanesultone (7.5 g; 0.055 moles). A waxy white solid wasisolated (1.57 g; 7% yield).

Preparation of FC-5; C₄F₉SO₂N(H)(CH₂)₃N⁺(CH₃)₂(CH₂)₃SO₃ ⁻

A 500 mL round bottom flask fitted with a condenser, heating mantle andstirrer under nitrogen atmosphere was charged withC₄F₉SO₂NH(CH₂)₃N(CH₃)₂ (15.0 g, 0.039 moles), 1,3-propanesultone (5.25g; 0.042 moles) and MTBE (100 mL) The mixture was held at refluxtemperature with stirring for 27 hours. After cooling to roomtemperature, the insoluble solid white product was isolated byfiltration of the MTBE suspension by suction through a sintered glassfrit and washing of the precipitate with three 100 mL portions of MTBE.The solid was dried partially by suction and then further dried in avacuum oven at 50-80° C., 10⁻² Torr for about 45 minutes. A white solidwas isolated (18.36 g; 93% yield).

Preparation of FC-6; C₄F₉SO₂NH(CH₂)₃N(CH₃)₂

A three-necked 2-liter round bottom flask equipped with an overheadstirrer, heating mantle, thermocouple, addition funnel, and refluxcondenser, was charged with DMAPA (642 g; 6.29 moles) and hexane (2000g). With agitation, 992 g of fractionated PBSF (992 g; 3.28 moles;fractionated 99% assay) was added over a period of one hour. The batchwas stirred at 50° C. for another 2 hours, then a Dean-stark trap wasinserted between the flask and the condenser. Water was addedportion-wise and the hexane removed by distillation. The flask wascooled to 21° C. and the batch allowed to settle for 15 minutes. Theliquid portion was removed using a 10 cm, 70 micron porous polyethylenerod (1.3 cm diameter), under vacuum. After washing twice with 2000 g ofwater, a wet, white solid cake was isolated and allowed to dry at roomtemperature overnight, followed by 3 hours at 90° C. A white solid wasisolated: (C₄F₉SO₂NH(CH₂)₃N(CH₃)₂, 1155 g; 91%).

Preparation of FC-7; C₄F₉SO₂N[CH₂CH(OH)CH₂SO₃Na](CH₂)₃N(CH₃)₂

A 1 L round bottom flask fitted with a heating mantle and condenser wascharged with C₄F₉SO₂NH(CH₂)₃N(CH₃)₂ (119.0 g; 0.31 moles), CHPS (62.5 g;0.32 moles), NaOH (13.3 g; 0.34 moles; pellets) and deionized water (250mL). The flask was heated at 95° C. overnight, resulting in a solidshown to be: C₄F₉SO₂N[CH₂CH(OH)CH₂SO₃Na](CH₂)₃N(CH₃)₂.

Preparation of FC-8; C₄F₉SO₂N[CH₂CH(OH)CH₂SO₃Na](CH₂)₃N⁺[CH₂CH(OH)CH₂SO₃⁻](CH₃)₂

The procedure described for Preparation of FC-7 was essentiallyfollowed, substituting the following amounts of materials:C₄F₉SO₂NH(CH₂)₃N(CH₃)₂ (59.5 g; 0.16 moles), CHPS (62.5 g; 0.32 moles),NaOH pellets (13.3 g; 0.34 moles) and deionized water (250 mL),resulting in a solid shown to be the above salt.

Preparation of FC-9; C₄F₉SO₂N(Me)CH₂CH(OH)CH₂SO₃Na

The procedure described for Preparation of FC-7 was essentiallyfollowed, substituting the following amounts of materials: C₄F₉SO₂NHMe(90.8 g; 0.29 moles), CHPS (62.5 g; 0.32 moles), NaOH pellets (12.5 g;0.30 moles) and deionized water (100 mL), resulting in a white solidshown to be: C₄F₉SO₂N(Me)CH₂CH(OH)CH₂SO₃Na.

Preparation of FC-10; C₄F₉SO₂N(Et)CH₂CH(OH)CH₂SO₃Na

A one liter flask equipped with an overhead stirrer, thermocouple,reflux condenser and heating mantle was charged with C₄F₉SO₂NHEt (92.0g; 0.28 moles), NaOH pellets (0.14 g; 0.35 moles) and deionized water(90 mL) and held at 98° C. for 5 hours. The batch was cooled to 76° C.and CHPS (69.0 g 0.35 moles), and deionized water (20 mL) were added.The batch temperature was increased to 100°C. and maintained for 18hours. The set point was lowered to 90° C. and deionized water (150 mL)was added. The batch was allowed to cool with stirring to 40° C. A whitesolid had formed in the bottom of the flask, and stirring was stoppedand the solid was allowed to settle.

When the batch temperature reached 30° C., the upper liquid was decantedfrom the white solid. Deionized water (250 mL) was added and the batchwas heated to 50° C. The flask was cooled to 19° C. and allowed tosettle. The upper liquid layer was decanted from the white solid on thebottom of the flask. Deionized water (200 mL) was added and the batchwas slurried at room temperature, and then filtered: The cake of whitesolid was washed with deionized water (100 mL), then dried to giveC₄F₉SO₂N(Et)CH₂CH(OH)CH₂SO₃Na (119 g; 88% yield). NMR, gc/ms and lc/msof an aliquot that had been acidified and treated with diazomethane wereconsistent with the desired structure.

Preparation of FC-11; _n-C₄F₉OC₄H₈SO₃K

A 600 mL Parr stainless steel reactor, available from Parr, Chicago,Ill., was charged with diglyme (130 g), Adogen™ 464 (8.0 g), KF (38 g;0.65 moles), n-perfluorobutyryl fluoride (130 g; 0.440 moles; 90%purity), and butane sultone (100 g; 0.73 moles). The reactor was heatedto 75° C. for 70 hours. The mixture was cooled, treated with 45% KOH andprecipitated with toluene. Structure of the resulting solid,n-C₄F₉OC₄H₈SO₃K (184 g, 92% purity), was confirmed using ¹³C- and ¹H-nmranalyses.

Preparation of FC-12; i-C₄F₉OC₄H₈SO₃K

The method described in Preparation 11 was essentially followed,substituting the following charges: diglyme (110.0 g), Adogen™ 464 (7.0g), KF (35.0 g; 0.60 moles), butane sultone (73.0 g; 0.54 moles ) andreplacing n- perfluorobutyryl fluoride with iso-perfluorobutyrylfluoride (175.0 g; 0.461 moles 70% purity). Structure of the resultingsolid, i-C₄F₉OC₄H₈SO₃K, was confirmed using ¹³C- and ¹H-nmr analyses.

Preparation of FC-13; n-C₄F₉OC₃H₆SO₃K

The method described in Preparation 11 was essentially followedsubstituting the following charges: n-perfluorobutyryl fluoride (166.0g; 0.562 moles; 90% purity), diglyme (150.0 g), Adogen™ 464 (9.0 g), 35g KF (47.0 g; 0.81 moles), and replacing butane sultone with propanesultone (81.0 g; 0.66 moles). Structure of the resulting solid,n-C₄F₉OC₃H₆SO₃K, was confirmed using ¹³C- and ¹H-nmr analyses.

Preparation of FC-14;C₄F₉SO₂N(C₂H₄OH)CH₂CH(OH)CH₂SO₃Na/C₄F₉SO₂NH(C₂H₄OH) mixture

A 500 mL round bottom flask equipped with a condenser, heating mantleand stirrer was charged with C₄F₉SO₂NH(C₂H₄OH) (9.05 g, 26.4 mmole; asprepared above) sodium hydroxide (1.1 g, 27.5 mmole) and deionized water(83.8 g) to form a clear homogeneous solution. CHPS (5.7 g, 29.0 mmole)was added in one portion and the ensuing mixture heated to 95° C. withstirring under a nitrogen atmosphere for 16 hours.

The resulting tan, viscous solution was cooled to room temperature andadditional water added to make a mixture of about 10% solids by weight.The structure of the product was confirmed by negative electrospraylc/ms which identified two primary components: C₄F₉SO₂NH(C₂H₄OH) (as thesodium salt, m/e=342) and C₄F₉SO₂N(C₂H₄OH)CH₂CH(OH)CH₂SO₃Na (m/e=480).Further quantitative analysis showed that 53% of the C₄F₉SO₂NHC₂H₄OHremained.

Preparation of FC-15; C₄F₉SO₂N(−)CH₂CH₂OH (K⁺)

C₄F₉SO₂NH CH₂CH₂OH (20.1 g; 0.059 moles; as prepared above), KOH (3.9 g;0.059 mole; 85%) and deionized water (66.0 g) were stirred at roomtemperature for 30 minutes until a relatively homogenous solution wasformed. The pH was 12-13. The solution was filtered to give 89 g of25.3% solids aqueous solution of C₄F₉SO₂N(−)CH₂CH₂OH+K.

Preparation of FC-16; C₄F₉SO₂N(C₂H₄OH)CH₂CH(OH)CH₂SO₃Na

A 1 L round bottom flask fitted with a mechanical stirrer, condenser,thermocouple and heating mantle was charged with C₄F₉SO₂NH(CH₂CH₂OH)(77.6 g; 0.226 moles), CHPS (56.0 g; 0.28 mole) and deionized water (80mL). The mixture was heated at 98° C. for 5 hours, cooled to 76° C. andNaOH was added (11.3 g; 0.28 moles). The batch temperature was increasedto 100° C. and maintained for 18 hours. The temperature was then loweredto 90° C. and a mixture of water/acetone (75 g/120 g) was added. Thebatch was allowed to cool with stirring to 40° C., then poured out intoa glass pan and dried at 50-60° C. overnight. The pan contained anoff-white solid (133 g) determined to beC₄F₉SO₂N(C₂H₄OH)CH₂CH(OH)CH₂SO₃Na. Structure was confirmed usingstandard lc/ms techniques.

Preparation of FC-18; C₄F₉SO₂NHC₆H₅

A 600 ml steel autoclave equipped with a paddle stirrer was charged withaniline (18.6 g; 0.2 mole), triethylamine (60.0 g; 0.6 mol) and PBSF(68.4 g; 0.23 mol). The ensuing mixture was stirred and heated at 120°C. for about 5 hr. The cooled reactor contents were mixed with NaOH (70g; 50% aq) and warmed to about 50° C. for a few hours. The mixture wasthen acidified with sulfuric acid (50%) and the resulting dark oilextracted into methylene chloride. The solvent was evaporated and theresidual 50.4 g was distilled to yield a tan, waxy solid (30.2 g; b.p.95-110° C./0.15 mm Hg (20 Pa)). Recrystallization from hexane gave lighttan crystals, mp 60-63° C.

Preparation of C₄F₉SO₂N(C₃H₇)CH₂CH(OH)CH₂SO₃Na (FC-19)

A 1 L 3-necked round bottom flask equipped with a condenser, mechanicalstirrer, thermocouple and addition funnel was charged withperfluorobutanesulfonyl fluoride (100.0 g; 0.33 moles). n-Propyl amine(40.0 g; 0.68 mole) was then added over a period of 30 minutes. Theensuing mixture was refluxed at 72° C. for 2 hours at which time water(300 mL) was slowly added. The batch was stirred for about 15 minutesand the upper aqueous phase was removed an discarded. The remainingmaterial was then successively washed with 5% sufuric acid (300 mL; 5%;aq) and water (300 mL). The viscous yellow liquid recovered was shown tobe C₄F₉SO₂NHC₃H₇ (99 g).

A 1 L 3-necked round bottom flask equipped with a mechanical stirrer,thermocouple, reflux condenser and heating mantle was charged withC₄F₉SO₂NHC₃H₇ (93.6 g; 0.27 moles; as prepared above), NaOH (13.6 g;0.35 moles; pellets) and water (90 mL) and heated at 98° C. for 45minutes. Upon cooling to 76° C., CHPS (67.5 g; 0.34 moles) was added andthe temperature was then increased to 100° C. and maintained for 18hours. Water was then added (250 mL) and a viscous yellow liquid formedin the bottom of the flask. The upper liquid phase was decanted off anddiscarded leaving a thick yellow liquid, to which water (250 mL) wasadded. The temperature of the mixture was increased to 50° C., thencooled to 19° C. Upon removal of water a créme colored solid remained,C₄F₉SO₂N(C₃H₇)CH₂CH(OH)CH₂SO₃Na (111.4 g; 81% yield).

The surface tension at a 0.2 wt. % in 85% phosphoric acid was 19.4dynes/cm.

Preparation of Buffered Oxide Etch Examples and Comparative Examples

A premix of each surfactant was made to facilitate the addition of thesurfactant to the 500:1 BOE solution. Premixes nominally contained 2%surfactant by wt. in water alone, a mixture of isopropanol/deionizedwater (3:1 by wt.), or a mixture of water,isopropanol/n-butanol/deionized water (5.4:1.7:1 by wt.). Table 1. Thefluorochemical premix was added to a buffered oxide etch solution (BOE500:1 Buffered oxide etch solution; available from Ashland Chemical,Dublin, Ohio) in an amount such that the resulting surfactantconcentration was 500 ppm, unless otherwise noted in Table 1.

Surface tension measurements were then made on the unfiltered andfiltered solutions (Vacuum Filter/Storage Systems, Sterile 0.22 micronPES Membrane, 50 mm filter diameter, 250 mL Receiver cap; available fromCorning, Corning, N.Y.) according to Test Procedure I: Surface TensionDetermination described above.

TABLE 1 Surface tension values (dyne/cm) for 500:1 BOE solutionscontaining various surfactants at given concentrations. Surface Tensionin dyne/cm (post- Example Fluorochemical Premix Solvent filtration) C1none added none added 93.0 (93.0) C2 FC-23 DI Water 66.3 (66.9) C3 FC-17DI Water 39.2 (73.6) C4 n-octylamine (@ 1000 ppm) DI Water 22.7 (22.9)C5 Forfac ™ 1033D DI Water 45.6 (84.7) C6 CHPS DI Water 91.8 (—) 1 FC-1IPA/DI Water 28.7 (57.4) 2 FC-1 DI Water 24.6 (90.0) 3 FC-1IPA/n-butanol/ 25.8 (20.0) DI Water 4 FC-2 DI Water 46.4 (90.7) 5 FC-3DI Water 29.6 (89.3) 6 FC-4 DI Water 29.4 (29.5) 7 FC-5 DI Water 21.9(29.8) 8 FC-8 IPA/n-butanol/ 19.5 (22.0) DI Water 9 FC-8 DI Water 19.2(24.0) 10 FC-10 DI Water 17.7 (18.2) 11 FC-11 DI Water 17.3 (17.6) 12FC-13 DI Water 17.4 (18.0) 13 FC-10 IPA/n-butanol/ 18.0 (17.4) DI Water14 FC-14 DI Water 17.1 (17.2) 15 FC-10/FC-15 DI Water 17.4 (17.8) (1:1by wt) 16 FC-16 DI Water 26.3 (53.4) 17 FC-18 DI Water 27.4 (35.8)Preparation of Surfactant Solutions in Various Solvents

Solutions of surfactants (0.2% by wt) were prepared by the dissolutionof appropriate amounts of surfactant in the solvent listed in Table 2.Surface tension measurements were then made on the unfiltered solutionaccording to Test Procedure I: Surface Tension Determination describedabove. Results are listed in Table 2.

TABLE 2 Surface Tension (dynes/cm) for additive at 0.2% in solventExample Solvent FC-10 FC-14 FC-11 FC-7 FC-8 C7 DI water 30 24 24 42 2418 HCl 18 19 19 33 20 (18.5%) 19 HNO₃ 28 30 27 44 28 (40%) 20 H₂SO₄ 1817 18 33 21 (50%) 21 H₃PO₄ 19 24 20 * * 85% *not measured

1. An aqueous etch solution comprising: a) an acid, and b) a surfactantof the formula:R_(f)—Q—R¹—SO₃ ⁻M⁺ wherein R_(f) is a C₁ to C₁₂ perfluoroalkyl group, R¹is an alkylene of the formula —C_(n)H_(2n)(CHOH)_(o)C_(m)H_(2m)—,wherein n and m are independently 1 to 6, and o is 0 or 1, and isoptionally substituted by a catenary oxygen or nitrogen group; M⁺ is acation; and Q is —O—, or —SO₂NR²—, wherein R² is an H—, alkyl, aryl,hydroxyalkyl, aminoalkyl, or sulfonatoalkyl group, optionally containingone or more catenary oxygen or nitrogen heteroatoms.
 2. The etchsolution of claim 1 wherein said alkyl, hydroxyalkyl, sulfonatoalkyl oraminoalkyl groups of said —SO₂NR²— group have from 1 to 6 carbon atoms.3. The etch solution of claim 2 comprising 0.1 to 49 weight percent HFor onium fluoride complex thereof.
 4. The etch solution of claim 1wherein said hydroxyalkyl group is of the formula —C_(p)H_(2p)—OH, wherep is an integer of 1 to
 6. 5. The etch solution of claim 1 wherein saidaminoalkyl group is of the formula —C_(p)H_(2p)—NR³R⁴ where p is aninteger of 1 to 6 and R³ and R⁴ are independently H or alkyl groups ofone to six carbon atoms.
 6. The etch solution of claim 1 wherein saidacid is HF or an onium fluoride complex.
 7. The etch solution of claim 6wherein said hydrogen fluoride complex is selected from pyridiniumpoly(hydrogen fluoride), oxonium poly(hydrogen fluoride), ammoniumpoly(hydrogen fluoride), and phosphonium poly(hydrogen fluoride).
 8. Theetch solution of claim 1 wherein R_(f) is a C₃ to C₆ perfluoroalkylgroup.
 9. The etch solution of claim 1 wherein said cation is an alkalimetal, an alkaline earth metal, a transition metal, or an onium ion. 10.The etch solution of claim 7 wherein said onium ion is an ammonium ion.11. The etch solution of claim 1 wherein said R¹ group is—C_(n)H_(2n)CH(OH)C_(m)H_(2m)—, wherein n and m are independently 1 to6.
 12. The etch solution of claim 1 comprising 10 to 1000 parts permillion of said surfactant.
 13. The etch solution of claim 1 comprising100 to 500 parts per million of said surfactant.
 14. The etch solutionof claim 1 further comprising a perfluoroalkylsulfonamido salt.
 15. Theetch solution of claim 14 wherein said perfluoroalkylsulfonamido salt isof the formula:R_(f)—SO₂N⁻—R⁶⁻M⁺ wherein R_(f) is a C₁ to C₁₂ perfluoroalkyl group, R⁶is H, an alkyl group, a hydroxyalkyl group or an aminoalkyl group, andM+ is a cation.
 16. The etch solution of claim 1 comprising HF andammonium fluoride.
 17. The etch solution of claim 16 comprising 0.1 to10 weight % HF and 20 to 40 weight % of ammonium fluoride.
 18. The etchsolution of claim 1 having a surface tension of 23 dynes/cm or less. 19.The etch solution of claim 1 comprising surfactants of the formula:

wherein R_(f), R¹ and M⁺ are as defined in claim 1, p is 1 to 6, and Zis H, aryl, —OH, —SO₃ or —NR³R⁴, where R³ and R⁴ are independently H oralkyl groups of one to six carbon atoms.
 20. The etch solution of claim1 comprising surfactants of the formula:

wherein R_(f) is a C₁ to C₁₂ perfluoroalkyl group, R¹ is an alkylene ofthe formula —C_(n)H_(2n)(CHOH)_(o)C_(m)H_(2m)—, wherein n and m areindependently 1 to 6, and o is 0 or 1, and is optionally substituted bya catenary oxygen or nitrogen group, and M⁺ is a cation.
 21. The etchsolution of claim 1 comprising a mixture of said surfactants.
 22. Theetch solution of claim 1 wherein said R¹ group contains a catenarynitrogen selected from —NR⁵— and —N(R⁵)₂ ⁺— wherein each R⁵ is a H—, ora C₁ to C₆ alkyl group.